The objective of these studies is to determine the changes in nucleic acid metabolism in the mouse uterus under conditions mimicking those of early pregnancy. The rates of incorporation of labeled precursors into different species of RNA are to be determined in vivo and in vitro, utilizing electrophoresis and hybridization methods for fractionating the RNA. The effects of intrauterine oil injection on the uterus of ovariectomized, hormone treated mice, with respect to RNA metabolism, will be determined. The effect of the decidualizing stimulus on other biochemical events that may play an intermediate role in the initiation of increased RNA synthesis will also be investigated. Some studies of the nature of the stimulus required for decidualization will also be done. At a later stage, the effects of early pregnancy itself on these various processes will be studied. These studies are directed toward a better understanding of the biochemical changes in the uterus at the time of implantation with the expectation that this will in turn be useful in developing new approaches to decreasing fertility.